See Ban ChatGPT network-wide for reference.
Briefly, ChatGPT is a language model that uses the statistics of words in a training dataset to generate grammatically correct responses to plain language prompts.
That means you could take a Stack Exchange question, put it into ChatGPT, and with no effort have a lengthy text answer generated.
The main problems with ChatGPT for a site like this are:
Attribution to ChatGPT is required, but most people using the content ignore this.
Nothing ensures the output is accurate, it's just based on a statistical model that can go horribly wrong at times. Worse, even wrong output is written in a way that can seem accurate/knowledgeable. ChatGPT is very good at "faking" answers, which means it takes far more human effort to identify bad ChatGPT answers, while it takes almost no effort to post one.
Nothing prevents ChatGPT from plagiarizing. It does not reference the material it is trained on, and very easily could lift entire passages from specific items in sufficiently niche areas.
Even if the sentences it produces are not lifted, ChatGPT doesn't reference the sources used, which is a requirement for most answers here.
No value is added. If someone wants to get an AI answer to their question, they can just go to ChatGPT and ask it themselves. Posting a ChatGPT answer is not really any different than pasting a question into Google and copying a list of the first several entries. If someone wants the first 5 results to a particular Google search they can just use Google.
For simplicity, I recommend we simply ban this content here. Moderators here can already remove ChatGPT-sourced content that infringes on existing site rules, and I doubt there will be many ChatGPT posts that meet our other standards, so this policy change won't really affect much except to make it clear and avoid any argument about what is and isn't acceptable.